Simple Bitwise Question...I hope

[mem0ri]

I've got a situation where...in the one case I'm setting a bitwise value $x:

$x = (2 << $y);

 

And another where I need to instead 'discover' the value of $y if $x is known instead...

 

$y = 2 ???? $x;

 

I could run a while loop....

 

while(($x/2) != 2) $z++;

 

But I'm wondering if someone might know another, more 'efficient' way of working out the equation?  It SEEMS like there must be an inverse relationship with << and >> that would allow you to figure how many bit's a number is shifted...

 

BTW...I'm using only factorial values in this area of the app...so all numbers would come out as 'clean' numbers like 2, 4, 8, 16, 32, etc.